1. Field of the Invention
The present invention relates to a lens array unit which may include one or more lens arrays used in an image reading apparatus for example. It also relates to a method of forming an image of an object to be read out.
2. Description of the Related Art
An image reading unit, incorporated in e.g. a facsimile machine, may be provided with an array of light receiving elements and with a lens array for focusing the light reflected on a document onto the light receiving elements. A typical example of a conventional lens array is shown in FIGS. 29 and 30 of the accompanying drawings. The illustrated lens array 9 includes a plurality of rod lenses (self-focusing lenses) 91 arranged in a line, and a resin holder 90 for holding the rod lenses 91. Each of the rod lenses 91 has a pair of flat lens surfaces 91a-91b, and its refractive index varies in accordance with the distance from the central axis. Thus, as shown in FIG. 30, light passing through the rod lens 91 follows a meandering path, whereby the image of an object (bxe2x86x92a) is projected in a non-inverting and non-magnifying manner (bxe2x80x2xe2x86x92axe2x80x2).
The lens array 9 may be fabricated in the following manner. First, the rod lenses 91 are produced. Then, the holder 90 is made of a resin material, with the rod lenses 91 embedded therein.
Disadvantageously, the lens array 9 is rather expensive since the rod lenses 91, having the above-described special optical properties, are difficult to produce. Further, the productivity of the lens array 9 tends to be low due to the separate preparation and the subsequent assembling of the rod lenses 91 and the holder 90.
The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to make it possible to form a true image of an object with simpler and less expensive optical means than is conventionally possible.
According to a first aspect of the present invention, there is provided a lens array unit which comprises: a first lens array provided with a plurality of first convex lenses and a first transparent holder formed integral with the first lenses, each of the first lenses having first and second lens surfaces; a second lens array provided with a plurality of second convex lenses and a second transparent holder formed integral with the second lenses, each of the second lenses having third and fourth lens surfaces, the second lens array being attached to the first lens array so that the third lens surfaces face the second lens surfaces; and a light shield mounted on the first lens array and provided with a plurality of through-holes facing the first lens surfaces.
In this specification, a xe2x80x98convexxe2x80x99 lens refers to a lens including at least one convex lens surface. Thus, the other lens surface opposite to this convex lens surface maybe convex, flat or concave.
According to the present invention, each of the first and the second lens arrays can be readily produced by a conventionally known molding technique. In particular, each lens of the first or second lens array of the present invention is a simple convex lens, instead of a self-focusing lens which is rather expensive and difficult to fabricate. Thus, the lens array unit of the present invention is more readily made at a lower cost than the conventional rod lens array.
Preferably, the first and second lens arrays may cooperate to form a non-inverted and non-magnified image of an object. In this specification, xe2x80x98non-magnifiedxe2x80x99 means that the size of the projected image of the object is equal to the original size of the object.
Preferably, each of the through-holes may have a dark-colored inner wall surface. Advantageously, the inner wall surface is black. Simply, the light shield as a whole may be made of a dark-colored resin material.
For positioning purposes, the light shield and the first lens array may be provided with engaging means including a recess and a projection fitted into the recess.
Preferably, the light shield may be attached to the first lens array in a stretched state, so that the light shield is held in proper contact with the first lens array.
In a preferred embodiment, the light shield may include a plurality of segments connected to extend in a predetermined direction. Advantageously, any adjacent segments may overlap with each other in their thickness direction for preventing the passage of stray light. All of the segments may be equal in configuration and size to each other, considering the efficiency of production.
Preferably, each of the first lens surfaces may be convex and at least partially project into a relevant one of the through-holes of the light shield. In this manner, the alignment of the first lens array and the light shield is facilitated. Further, the positional deviation of the first lens array relative to the light shield is effectively prevented.
Preferably, the first lens surfaces may be diametrically greater than the through-holes of the light shield. With this arrangement, each first lens surface can be maintained in proper facing relation to the appropriate through-hole even if the first lens array and the light shield are slightly displaced relative to each other.
According to a second aspect of the present invention, use may be made of only one lens array for providing a lens array unit. In this case, the lens array unit may comprise: a lens array provided with a plurality of lenses and a transparent holder formed integral with the lenses, each of the lenses having first and second lens surfaces; and a light shield formed with a plurality of through-holes facing the first lens surfaces.
According to a third aspect of the present invention, there is provided a lens array unit comprising: a first lens array provided with a plurality of first convex lenses arranged in a line, each of the first lenses having first and second lens surfaces; a second lens array provided with a plurality of second convex lenses arranged in a line, each of the second lenses having third and fourth lens surfaces, the second lens array being attached to the first lens array so that the third lens surfaces face the second lens surfaces; and light shielding means for partially covering at least either one of the third and the fourth lens surfaces of each second lens.
Preferably, the light shielding means may comprise a dark-colored layer formed directly on at least either one of the third and the fourth lens surfaces of each second lens.
Preferably, the first lens array may be formed with grooves for optically separating the first lenses from each other. Advantageously, each of the grooves may be provided with a dark-colored light shielding member. The light shielding member may be a black layer covering the inner wall surfaces of each light separation groove, or black material filled in the light separation groove.
Preferably, each of the first and the second lens arrays may include a transparent holder formed integral with the lenses. The holder of the first lens array may include obverse and reverse surfaces spaced from each other in an axial direction of the first lenses, wherein the obverse and the reverse surfaces are covered with light shielding means.
Similarly, the holder of the second lens array may include obverse and reverse surfaces spaced from each other in an axial direction of the second lenses, wherein at least either one of the obverse and the reverse surfaces is covered with light shielding means.
According to a fourth aspect of the present invention, there is provided a lens array comprising: a plurality of lenses arranged in a line and each having a lens surface; and light shielding means for partially covering the lens surface. The lens surface may include peripheral portions spaced from each other along the above-mentioned line, wherein the light shielding means covers the peripheral portions.
According to a fifth aspect of the present invention, there is provided a method of forming an image of an object. The method may comprise the steps of: preparing a lens array unit which includes a first lens array provided with first lenses and a second lens array provided with second lenses, the first lens array being arranged closer to said object than the second lens array is, each of the second lenses having a light inlet surface and a light outlet surface; and partially shielding at least either one of the light inlet surface and the light outlet surface for adjusting brightness of light spots formed along a predetermined focal line.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.